The present invention pertains to a remote communication system, and, more particularly, to a radio frequency identification system and method for the transmission and reception at multiple frequencies of data stored on radio frequency identification tags.
Remote communication utilizing wireless equipment typically relies on radio frequency (RF) technology, which is employed in many industries. One application of RF technology is in locating, identifying, and tracking objects, such as animals, inventory, and vehicles.
RF identification (RFID) tag systems have been developed to facilitate monitoring of remote objects. As shown in FIG. 1, a basic RFID system 10 consists of three components, an antenna 12 or coil, a transceiver with decoder 14, and a transponder (commonly called an RF tag) 16. In operation, the antenna 12 emits electromagnetic radio signals generated by the transceiver 14 to activate the tag 16. When the tag 16 is activated, data can be read from or written to the tag.
In some applications, the antenna 12 is a component of the transceiver and decoder 14 to become an interrogator (or reader) 18, which can be configured either as a hand held or a fixed-mount device. The interrogator 18 emits the radio signals 20 in range from one inch to one hundred feet or more, depending upon its power output and the radio frequency used. When an RF tag 16 passes through the electromagnetic radio waves 20, the tag 16 detects the signal 20 and is activated. Data encoded in the tag 16 is then transmitted by a data signal 22 through an antenna 24 to the interrogator 18 for subsequent processing.
An advantage of RFID systems is the non-contact, non-line-of-sight capability of the technology. Tags can be read through a variety of substances such as snow, fog, ice, paint, dirt, and other visually and environmentally challenging conditions where bar codes or other optically-read technologies would be useless. RF tags can also be read at remarkable speeds, in most cases responding in less than one hundred milliseconds.
There are three main categories of RFID tags. These are beam-powered passive tags, battery-powered semi-passive tags, and active tags. Each operate in fundamentally different ways.
The beam-powered RFID tag is often referred to as a passive device because it derives the energy needed for its operation from the radio frequency energy beamed at it. The tag rectifies the field and changes the reflective characteristics of the tag itself, creating a change in reflectivity that is seen at the interrogator. A battery-powered semi-passive RFID tag operates in a similar fashion, modulating its RF cross section in order to reflect a delta to the interrogator to develop a communication link. Here, the battery is the source of the tag""s operational power. Finally, in the active RFID tag, a transmitter is used to create its own radio frequency energy powered by the battery.
A typical RF tag system 10 will contain at least one tag 16 and one interrogator 18. The range of communication for such tags varies according to the transmission power of the interrogator 18 and the tag 16. Battery-powered tags operating at 2,450 MHz have traditionally been limited to less than ten meters in range. However, devices with sufficient power can reach up to 200 meters in range, depending on the frequency and environmental characteristics.
Conventional RF tag systems utilize continuous wave backscatter to communicate data from the tag 16 to the interrogator 18. More specifically, the interrogator 18 transmits a continuous-wave radio signal to the tag 16, which modulates the signal 20 using modulated backscattering wherein the electrical characteristics of the antenna 24 are altered by a modulating signal from the tag that reflects a modulated signal 22 back to the interrogator 18. The modulated signal 22 is encoded with information from the tag 16. The interrogator 18 then demodulates the modulated signal 22 and decodes the information.
Conventional continuous wave backscatter RF tag systems can read but only one tag at a time in serial fashion. Because only a limited number of tags can be read over a given period of time, the amount of data the system can process over the period of time is restricted. In addition, the amount of information that can be transmitted from a single tag is limited due to the serial nature of conventional technology.
The present invention is directed to a multi-frequency communication system between a reader and one or more remote communication devices and a method related thereto. In accordance with one embodiment of the invention, a remote communication device is provided that includes a communication circuit configured to receive a first signal and to return a second signal responsive to the first signal, the second signal including a first modulation component and a second modulation component, the second modulation component having at least one data signal unique to the remote communication device. Ideally the first and second signals are radio frequency signals.
In accordance with another aspect of the present invention, the communication circuit includes at least one data signal generator for generating the second modulation component. Alternatively, the second modulation component can include first and second data signals generated by first and second data signal generators or by a variable frequency data signal generator.
In accordance with another embodiment of the present invention, a remote communication device is provided that includes an antenna for receiving at least a first signal and to return a second signal; and a processing circuit coupled to the antenna for generating the second signal in response to the first signal, the processing circuit having a modulation circuit for modulating the second signal at a primary frequency and at least one intermediate frequency (IF) that includes data unique to the remote communication device. Ideally, the first and second signals are radio frequency signals.
In accordance with another aspect of this embodiment of the invention, the primary frequency comprises first and second states and the intermediate frequency is imposed on the first state. Alternatively, the second signal comprises the primary frequency and first and second intermediate frequencies, with the first intermediate frequency imposed on the first state and the second intermediate frequency imposed on the second state.
In accordance with another embodiment of the present invention, a reader for communicating with a plurality of remote communication devices at multiple IF frequencies is provided. The reader includes an antenna for receiving a plurality of remote signals at multiple IF frequencies; and a first receiving circuit coupled to the antenna for simultaneously extracting data from each of the remote signals. Ideally, the receiving circuit comprises a plurality of processing circuits for extracting data from each of the remote signals, each of the plurality of processing circuits configured to process a remote signal of a predetermined frequency.
In accordance with another aspect of this embodiment of the invention, a second receiving circuit is provided for simultaneously extracting data from each of the remote data signals that are not received in the first receiving circuit, such as due to phase shifting, such as from quadrature nulls.
In accordance with another aspect of this embodiment of the invention, the reader includes a transmitting circuit coupled to the antenna for transmitting an interrogation signal to the remote communication devices. In one embodiment the antenna includes a transmitting antenna and a receiving antenna. Optionally, a low noise amplifier is coupled between the receiving antenna and the first and second receiving circuits.
In accordance with another aspect of this embodiment of the invention, the first receiving circuit includes a first processing circuit for extracting an intermediate frequency signal and a second processing circuit for extracting data from the intermediate frequency signal.
In accordance with yet another embodiment of the present invention, a multi-frequency communication system for communicating with a plurality of remote communication devices is provided. The system includes a plurality of remote communication devices, each device configured as described above, and a reader for communicating with a plurality of remote communication devices at multiple IF frequencies, as described above.
In accordance with another embodiment of the invention, a method for multi-frequency communication between a plurality of remote communication devices is provided, the method including receiving an interrogation signal at the plurality of remote communication devices; generating a remote signal responsive to the interrogation signal at each remote communication device, the remote signal having an IF frequency that may be unique to the remote communication device; and receiving the remote signals; and extracting data from the remote signals.